Safety hooks are known which comprise a closing pawl hinged on the body of the hook and provided with a connection hole at its outer end. When a load is raised with a hook of this type, its effect is to cause the pivoting of the pawl and to apply it onto the nose of the hook, the load being thus prevented from coming off the hook. A latch provided with a return spring permits the immobilization of the pawl in its closing position. Such hooks are described in particular in French Pat. No. 1,574,978.
Safety hooks as described above have a special shape. In particular, their nose is shorter than that of a normal hook, so that, if the closing pawl is not in the closed position, the load may easily slip and come off the hook. When the load is engaged on the hook, it is possible that, as a consequence of friction, the load might not come to the bottom of the opening of the hook, and might remain in the vicinity of the end of the nose. When subsequently, the hook is raised with its load, it assumes a position in which the connection hole and the point of action of the load on the hook lie along the same vertical; the load thus remains in the vicinity of the end of the nose, which is dangerous, especially if the pawl is not in its fully closed position. Even if the pawl is in this position, it is possible that the return spring may be broken so that the latch does not prevent the pawl from freeing the opening of the hook. There is also nothing to indicate to the user that the latch is in a working condition and has really locked the pawl in its closed position.
There is also known from U.S. Pat. No. 4,007,957 a hook fitted with a latch which has two opposed noses and which is pivotally mounted on the upper part of the hook body, about an axis situated along the plane of said hook and horizontal in the normal position of use of the latter, so as to be able to occupy a safety position in which one of its noses is situated in the vicinity of the nose of the hook. However, no means are provided to lock the latch in its safety position. If the latch happens to pivot at the wrong moment, the load may escape from the hook. This known hook does not truly constitute a safety hook.